**title** Asp Conference Series, Vol. **volume**, **publication Year** **editors** Five Years of Observations with the Chandra X-ray Observatory

The Chandra X-ray Observatory is the X-ray component of NASA's Great Observatory Program and has been operating successfully for over five years. We present here brief overview of the technical performance and some of the remarkable discoveries. Placement in its highly elliptical orbit was completed 15 days after launch. The orbit has a nominal apogee of 140,000 km and a nominal perigee of 10,000 km. With this orbit, the satellite is above the radiation belts for more than about 75% of the 63.5-hour orbital period and uninterrupted observations lasting more than 2 days are possible. The observing efficiency, which also depends on solar activity, has varied from 65% to more than 70%. The spacecraft has been functioning superbly since launch. The specified design life of the mission was 5 years; however, the only perishable is gas for maneuvering and is sized to allow operation for much more than 10 years. The orbit will be stable for decades. One of the most important functions of the Observatory subsytems is to provide the absolute accuracy of Chandra X-ray source locations. Based on observations of 225 point sources detected within 2 ′ of the boresight and having accurately known coordinates, the 90% source location error circle has a radius of 0.64 ′′ and fewer than 1% of sources are outside a 1 ′′ radius. There is also an effective blurring of the X-ray point spread function (PSF) due to uncertainties in determining the aspect solution. An indirect method of estimating aspect blurring uses the aspect solution to " de-dither " the aspect camera's star images and measure the residual jitter. Based on a sample of 350 observations one finds that 99% of the time the effective blurring is less than 0.20 ′′ (FWHM). The heart of the Observatory is the X-ray telescope made of four concentric, precision-figured, superpolished Wolter-1 telescopes, similar to those used for both the Einstein and Rosat observatories, but of much higher quality, larger diameter, and longer focal length.